An organic EL light source device is an element in which an organic light-emitting layer is provided between a plurality of electrode layers to electrically obtain light emission. Organic EL light source devices have been studied regarding its use as a display element in place of a liquid crystal cell. Further, the use of organic EL light source devices as a surface light source, such as a backlight for flat-type illumination or for a liquid crystal display device, that utilizes the characteristics of a high luminous efficiency, low voltage drive, light weight, low cost and the like, is also being studied.
One issue when using an organic EL light source device as a surface light source is how to efficiently extract light in a useful form from the organic EL light source device. For example, although the light-emitting layer of the organic EL light source device itself has a high luminous efficiency, the light amount decays due to interference and the like in the layers during the light passes through the layered structures of the device and emitted therefrom. Thus, this loss of light needs to be as small as possible.
As a method for increasing light extraction efficiency, for example, Patent Literature 1 discloses improvement of the overall brightness by suppressing the brightness in the frontal direction(0°) of the device and increasing the brightness at angles of 50 to 70°.